The present invention relates to an ignition apparatus for an internal combustion engine, and more particularly to a cylindrical type ignition apparatus housed in a spark plug hole of an engine cylinder.
An example of the conventional ignition apparatus for an internal combustion engine is disclosed in Japanese Utility Application Laid-Open No. 2-92913, in which iron cores which form a closed magnetic path is housed inside a cylindrical plastic case, primary and secondary coils are fitted outside the iron core and their periphery is hardened with insulating resin, and an outer iron core is incorporated along a wall of the cylindrical plastic case. Because a lot of leakage magnetic flux occurs during energization of the primary coil in such a prior art, it is impossible effectively to utilize the magnetic flux generated by the primary coil. To obtain the desirable power, it is required to enlarge the cross-sectional area or increase the number of turns of the primary coil. Therefore, the ignition apparatus becomes large as an inevitable consequence.
Accordingly, the conventional ignition apparatus is not suitable to a cylindrical type ignition apparatus housed in a plug hole of an engine cylinder head and connected directly to a spark plug.